Vauxhall Corsa Twist Immobiliser Fault?

I have a 1995 Vauxhall Corsa Twist, i only bought it 2 days ago as a little run around, now i can't get it to start..It has an Immobiliser which is a little back fob (not on the key) that you slot into the dash, then i should be able to start the car, well when the woman showed me how to use it, she quickly put the fob in the slot took it out and started it up no problem, ive tried so many combinations to start the thing up, all the lights work so im guessing its not the battery and the radio comes on, it doesnt attempt to turn over at all, is there a knack to it? im at a loss..any way to bypass it if i cant get it started? would this cost alot? any help would be fantastic